Wet wall problem. Is there aircon drain pipe or a water pipe in those walls? Or is that wall next to the toilet?

Usually need to scrape/sand down to bare cement and apply sealer/primer then only paint over with topcoat (colour paint) 2 coat.
5-6 coat seems dodgy like they tryna hide something.

I used bosch orbital sander with lots of rough sandpaper discs to sand down 30 year old paint coz old paint comes off the moment you roll on it (gunked up instantly the rollers).
The sanding looked like Iraq desert storm. Required 3M full cup N95 to breathe.

As you mentioned it happens on all walls.. does the whole house have adequate ventilation or its Tupperware style (windows never open)?
Suspect that there's more to this than meets the eye as the dampness may also be due to roof leaking (walls sponging up the water).

Are the walls esp affected area damp/cold when touched?
Plaster sound when knocked?

https://www.bottompaintstore.com/blog/tag/paint-chalking/

I think what happened was you got frosting problem.

FROSTING:
A white, salt-like substance on the paint surface. Frosting can occur on any paint color, but it is less noticeable on white paint or lighter tints. On masonry, it can be mistaken for efflorescence (see Efflorescence and Mottling).

POSSIBLE CAUSES: Forms mostly in protected areas (such as under eaves and on porch ceilings) that do not receive the cleansing action of rain, dew and other moisture. Use of dark-colored paints that have been formulated with calcium carbonate extender.

Application of a dark-colored paint over a paint or primer containing calcium carbonate extender.

SOLUTION: Frosting can be a stubborn problem. It often cannot be washed off readily. Moreover, the condition can recur even as a bleed-through when a new top coat is applied. In extreme cases, it can interfere with adhesion. The best remedy is to remove the frosting by wire brushing masonry or sanding wood surfaces; rinse, then apply an alkyd-based primer before adding a coat of high quality exterior paint.

Removal by sanding down to bare cement plaster, wipe down whole wall using bucket and some soap solution with old t shirt/rags until not powdery, then use primer (nippon 5100/5400), then finish topcoat (colour paint x2 coat) will solve the issue. Looks like because old paint still there the problem never go away.

Basic sander without dust bag, uses sheet sandpaper (the rougher the better)
https://www.lazada.com.my/products/corated-...2-s2719085.html

Atas sander with dust bag:
https://www.lazada.com.my/products/bosch-ge...s170092766.html
https://www.lazada.com.my/products/dewalt-d...s100004558.html

both will create iraq desert storm level of dust, move out everything from the room before start sanding.
Hand sanding will be extreme level workout.
Would recommend at least the basic sander plus maybe 20-30 sheets of sandpaper. Even bosch brand sandpaper only RM1/ea at CSM 225 PJ